1. Field of the Invention
This invention relates to heat setting powder lacquers. More especially this invention relates to heat setting powder lacquers comprising branched hydroxyl group containing polyester resins and titanium chelates. The heat setting powder lacquers of the present invention comprise branch hydroxyl group containing polyester resins which are solid at room temperature and titanium chelates which are also solid at room temperature. The powder lacquer composition can also contain pigments, leveling agents and/or conventional additives.
2. Discussion of the Prior Art
Powder lacquers made of branched polyester resins containing hydroxyl groups and melting above about 80.degree. C., and isocyanates capped with phenol, .epsilon.-caprolactam or other blocking agents as crosslinking agents, are known; cf. K. Weigel, "Polyester-Pulverlacke und ihre Verwendung im Lichtmetallbau," Fette, Seifen, Anstrichmittel 76 (1974), 170-174. These can be applied to the substrate by the known electrostatic powder spraying process or the also known fluidized bed sintering process, or also by dip lacquering from the melt, and they can be set by heating at temperatures above 130.degree. C., preferably above about 150.degree. to about 210.degree. C. to form level lacquer films which are resistant to chemical and physical stresses.
However, appreciable amounts of the capping agents used for the blocking of the isocyanates are liberated in these processes, thereby polluting the environment.
When known powder lacquers made from hydroxyl-group-containing polyester resins on the one hand and melamine or benzoguanamine resins on the other hand, are crosslinked by heating in the above-stated temperature range, cleavage products are released which can pollute the environment. In addition, such powder lacquers do not have sufficient shelf life at 40.degree. to 50.degree. C.
The setting of the powder lacquers prepared from a polyester resin component containing hydroxyl groups and one containing carboxyl groups, which are known through German "Auslegeschrift" No. 1,913,923, requires temperatures of 220.degree. C. and baking times of at least 15 minutes, which is uneconomical.
The powdered, heat-setting coating agents known through German "Auslegeschrift" No. 1,519,155, composed of polyesters containing hydroxyl groups and pyromellitic acid dianhydride (PMDA) also produce, after at least 30 minutes at 220.degree. C., coatings of low gloss. As much as 20 wt.-% of PMDA, with respect to the polyesters, is required.
Lastly, it is also known to harden hydroxyl-group-containing polyesters which are suitable as binding agents for powder lacquers by baking them with approximately 4 wt.-% of tetramethyltitanate, commercially known as VERNETZER MT. For this purpose, however, at least 15 minutes at 240.degree. C. are required, and the lacquer films obtained have Lange gloss ratings of no more than 85.
It is an object of this invention therefore to provide a powder lacquer composition which is solid at room temperature and which has an acceptable shelf life at 40.degree. C. to 50.degree. C. and which under the conditions of use does not release pollutants to the environment. It is a further object of this invention to provide a powder lacquer composition which can be applied to substrates at temperatures well below 240.degree. C. over a short period of time to provide lacquer films having Lange gloss ratings of at least 100.